METHOD OF PRODUCING THICK-SHEET STEEL AND STEEL TUBES FOR SUPER STRONG PIPELINE Russian patent published in 2012 - IPC C21D8/02 C21D8/10 C21D9/08 C21D9/50 C22C38/14 

FIELD: metallurgy.

SUBSTANCE: thick-sheet steel for super strong tubes is produced from steel that contains the following components in wt %: 0.03-0.08 C, 0.01-0.50 Si, 1.5-2.5 Mn, 0.01 or less P, 0.0030 or less S, 0.0001-0.20 Nb, 0.0001-0.03 Al, 0.003-0.030 Ti, less than 0.0003 B, 0.0010-0.0050 N, 0.0050 or less O, iron and unavoidable impurities making the rest. Fused steel is cast into slab to be hot rolled to make thick-sheet steel to be water cooled. Water cooling is performed to preset temperature above that of the start of M_s-point martnensitic transformation. Thick-sheet steel surface is, then, cooled by reiteration of processing whereat heat is recovered one or more times to cool is finally to M_s point or lower. UO-press is used to form tube from sheet. Sheet adjoining edges are arc-welded at flux using welding wire and agglomerated or fused flux to expand the tube.

EFFECT: tensile strength increased to 625 MPa, excellent low-temperature toughness.

10 cl, 3 tbl, 3 dwg